Why DD DUMMY,DSN=XXX is used ?

amajhi · New User Joined: 21 Jul 2006 Posts: 18 Location: Pune

Hi,

I am looking into one JCL and found for one of the DD statement it is coded as :

DD DUMMY,DSN=(DSNNAME),DISP=(NEW,CATLG,DELETE)

So can any one plz expain why DSN name is given along with DUMMY ?

superk · Posted: Tue Jul 20, 2010 3:19 pm

I have no idea, unless it was coded like that in a PROC.

Maybe the coder just wanted to document what dataset that DD used to use?

amajhi · New User Joined: 21 Jul 2006 Posts: 18 Location: Pune

In the JCL it is mentioned as :

//G.DM4 DD DUMMY,DSN=Dsnname,DISP=(NEW,CATLG,DELETE),
// UNIT=SYSDA,SPACE=(CYL,(1,1)),
// DCB=(RECFM=FB,LRECL=80,BLKSIZE=23440)

While DM4 is an output file.

amajhi · New User Joined: 21 Jul 2006 Posts: 18 Location: Pune

I think job will not create new file rather it will treat that DD as Dummy one.

PeterHolland · Posted: Tue Jul 20, 2010 4:02 pm

One use of the DUMMY parameter is in testing a program. When testing is finished and you want input or output operations performed on the data set, replace the DD DUMMY statement with a DD statement that fully defines the data set.

Another use of the DUMMY parameter is in a cataloged or in-stream procedure. Code on the DD DUMMY statement all the required parameters. When the procedure is called, nullify the effects of the DUMMY parameter by coding on the DD statement that overrides the DD DUMMY statement a DSNAME parameter that matches the DSNAME parameter on the DD DUMMY statement. For example, procedure step PS contains the following:

//DS1 DD DUMMY,DSNAME=A,DISP=OLD

Nullify the DUMMY parameter by coding:

//JS EXEC PROC=PROC1
//PS.DS1 DD DSNAME=A

Anuj Dhawan · Posted: Tue Jul 20, 2010 5:39 pm

The DUMMY parameter specifies that no device is to be allocated to this DD statement and that no disposition processing or I/O is to be done. All other JCL parameters on a DUMMY DD statement have to be syntactically correct. Use the DUMMY parameter if you know you will not need a file in a job step.So by this,

Anuj Dhawan · Posted: Tue Jul 20, 2010 5:43 pm

expat · Posted: Tue Jul 20, 2010 5:47 pm

Anuj,

That looks like an override for a PROC

procstepname.DDname DD whatever info to follow

Anuj Dhawan · Posted: Wed Jul 21, 2010 9:55 pm

Yes expat that could be - my intention was to say (once I could get the answer from OP), with the piece of code shown, that the user wnats to treat DSN associated with DM4 (the ddname) as DUMMY.

Pete Wilson · Posted: Mon Aug 16, 2010 10:21 pm

I prefer to make the DUMMY a symbolic value so you don't have to change the PROC and just change the symbolic value in the execution JCL.

e.g.

Dummied
//JS EXEC PROC=PROC1,D='DUMMY,'
//DS1 DD &D.DSNAME=A,DISP=OLD

Undummied..
//JS EXEC PROC=PROC1,D=''
//DS1 DD &D.DSNAME=A,DISP=OLD